An automotive radiator for cooling a coolant of an engine is provided in front of the engine 5 as shown in FIG. 3. The radiator 4 has an upper tank 4a, a lower tank 4c and a radiating core 4b provided between the upper tank 4a and the lower tank 4c. The radiating core 4b has a plurality of tubes and fins thermally connected to the tubes. A fan apparatus 12 is provided between the radiator 4 and the engine 5 for blowing the cooling air toward the radiating core. The fan apparatus has a boss 2 which is rotated by the outer driving source such as an electric motor and a plurality of blades 1 which is connected on the outer surface of the boss 2. A fan shroud 3 is provided in such a manner that the fan shroud 3 surrounds the fan apparatus 1 so that the cooling air generated by the fan apparatus 1 is introduced toward the fan apparatus.
A condenser 6 condensing a refrigerant of an automotive air conditioner is provided in front of the radiator 4. A front grille 8 is opened at the front end portion of a hood 10 so that the air through the front grille flows toward the condenser 6 and the radiator 4. The reference numeral 7 shows automotive bumper, the numeral 9 shows a skirt portion.
Since the engine 4 requires cooling efficiency, the radiator 4 is also required effective heat exchanging function. Accordingly, the radiator 4 employs the radiating core 4b which has a louvered fin the pitch of which is very narrow in order to increase the effective heat exchanging area, so that the resistance of the air passing through radiator has increased.
Furthermore, since the air passes through the radiator 4 should also pass through the condenser 6, the total resistance of the radiator 4 and condenser 6 should be quite high. The opening area of the front grille 8 has been decreased in order to reduce the coefficiency of the resistance of the automobile resently, so that the resistance of the air introducing into the fan apparatus 1 has been increased.
The increment of the resistance of the air also increases the noise generated by the fan. The conventional type of the fan apparatus cannot decrease the noise.
After the present inventors had examined about the relationship between the resistance of the air introduced into the fan apparatus and the noise caused by the fan apparatus, the present inventors presumed that the air flow passing through fan apparatus is varied in accordance with the resistance of the air introduced into the fan apparatus. The present inventors observed the air flow on the surface of the blade under the situation that the resistance of the air introduced into the fan apparatus was varied. According to the observation of the present inventors, the air flow passing through the fan apparatus 12 is parallel with the axis of the boss 2 as shown by the allow F in FIG. 4 and the vibration of the tuft attached on the surface of the blade is small while the resistance of the air introduced into the fan apparatus is small.
The air passing through the fan apparatus 12 under such situation flows in such a manner that the air makes concentric circles as shown in FIG. 5. The allow R shown in FIGS. 4 and 5 indicates the rotating direction of the blade 1.
The air passing through the fan apparatus 12 curves outwordly as shown in FIG. 6, and the tuft attached on the inner end of the blade vibrates strongly while the resistance of the air introduced into the fan apparatus is high. As shown from FIG. 7 which shows one blade 1 of a plurality of blades of the fan apparatus 12, the air passing through the outer surface of the blade flows outwordly.
The angle of incidence .alpha. is deemed to be increased when the resistance of the air introduced into the fan apparatus is high. Since the angle of incidence relates to the fan noise and the fan performance, the stall is occurred when the angle of incidence becomes too large. The angle of incidence .alpha. is calculated as the angle between a line T tying the leading edge 1a and the training edge 1b of the blade 1 and a line F which indicates the air flow introduced into the blade 1 as shown FIG. 2. The letter .beta. designates a setting angle which is calculated as the angle between a line T and a line R which shows the rotating direction of the blade. The letter L designates chord length between the leading edge 1a and the trailing edge 1b. The setting angle .beta. of the conventional type of fan apparatus decreases from the bottom portion to the intermediate portion of the blade 1 and decreases from the intermediate portion to the top portion, of the blade, as described by line J in FIG. 9. The velocity of the air passing through the top portion of the blade increases when the setting angle .beta. of the blade at the top portion increases, so that the turbulence of the air around the top portion is ceased. The setting angle .beta. at the bottom portion of the blade 1 is increased in order to make the amount of the air passing through the bottom portion increases. However, since the angle of the incidence .alpha. becomes high in accordance with the increment of the resistance of the air introduced into the fan apparatus, the occurrence of the stall on the both inner end and the outer end of the blade is predicted, and which causes the noise at those areas.
As described above, the air flow flowing on the surface of the blade 1 curves outwardly when the resistance of the air introduced into the fan apparatus is increased. The sectional shape of the blade is so designed that the fan profile as shown in FIG. 10 (a) is at X--X portion of the FIG. 8 which is perpendicular to the wing axis 1. The sectional shape of the blade, however, cannot maintain the fan profile and is such an irregular shape that described in FIG. 10(b) along with XI--XI line of FIG. 8 which is parallel with the derection of the air flow when the resistance becomes high. The XI--XI line of FIG. 8 designates the direction of air flow when the resistance is high as shown in FIG. 7. Therefore, the air flow flowing along with XI--XI line cannot flow smoothly so that the burble is occurred.